Advanced Waste Heat Recovery in Industrial Fired-Heaters

ABSTRACT

A piping system for recovery heat energy from an exhaust gas in a heat recovery furnace, the piping system comprising a piping inlet, where the piping inlet transects a wall of a stack zone of the heat recovery furnace, a piping run, the piping run fluidly connected to the piping inlet, and a piping outlet, the piping outlet fluidly connected to the piping run, where the piping outlet transects the wall of the stack zone of the heat recovery furnace, where the piping system is positioned in a stack zone of the heat recovery furnace between a stack inlet and a stack outlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Non-Provisional patent application Ser. No. 15/901,472 filed on Feb. 21, 2018. For purposes of United States patent practice, this application incorporates the contents of the non-provisional patent application by reference in its entirety.

TECHNICAL FIELD

Disclosed are systems and methods for recovering heat energy. Specifically, disclosed are systems and methods for recovering heat energy from a flue gas stream to heat a process gas stream.

BACKGROUND

Industrial fired-heaters, or fired-furnaces, are used in many process units to increase the temperature of gas streams in the process. The fired-heaters burn fuel gas to drive the temperature increase in the gas streams. The products of the combustion reaction exit the fired-heaters and are released to atmosphere. This product gas, or flue gas, is at a high temperature and can contain polluting or regulating components, such as nitric oxides, sulfur oxides, carbon monoxide, carbon dioxide, and other gases.

Fired-heaters have efficiencies around 50 percent (%) resulting in large amounts of fuel gas being burned to sustain the temperatures needed for the gas streams, with the remaining heat wasted.

SUMMARY

Disclosed are systems and methods for recovering heat energy. Specifically, disclosed are systems and methods for recovering heat energy from a flue gas stream to heat a process gas stream.

In a first aspect, a piping system for recovery heat energy from an exhaust gas in a heat recovery furnace is provided. The piping system includes a piping inlet the transects a wall of a stack zone of the heat recovery furnace, a piping run fluidly connected to the piping inlet, and a piping outlet fluidly connected to the piping run, where the piping outlet transects the wall of the stack zone of the heat recovery furnace, where the piping system is positioned in a stack zone of the heat recovery furnace between a stack inlet and a stack outlet.

In certain aspects, the piping run is spiral piping includes helix-shaped pipe, where the piping inlet transects the wall proximate to the stack outlet of the heat recovery furnace, where the piping outlet transects the wall proximate to the stack inlet of the heat recovery furnace, and where there is a gap between the spiral piping and the wall. In certain aspects, the gap is less than 2 inches. In certain aspects, the piping run is wraparound piping, the wraparound piping includes a piping rise fluidly connected to the piping inlet, where the piping rise has a rise height, a piping loop fluidly connected to the piping rise, where the piping loop is located adjacent to the wall, where the piping loop has a length and a piping down-run fluidly connected to the piping loop and further fluidly connected to the piping outlet, where the piping down-run has a down-run height. In certain aspects, the rise height is less than the distance between the stack inlet and the stack outlet. In certain aspects, the length of the piping loop is less than the perimeter of the stack zone. In certain aspects, the down-run height is less than the distance between the stack inlet and the stack outlet. In certain aspects, the piping system further includes two piping runs.

In a second aspect, a method of recovering heat from an exhaust gas in a stack zone of a heat recovery furnace is provided. The method includes the steps of introducing a process gas through a piping inlet, where the piping inlet transects a wall of the stack zone, allowing the process gas to flow through a piping run physically connected to the piping inlet, where the piping run is positioned in the stack zone between a stack inlet and a stack outlet, where the piping run is positioned adjacent to the wall such that the exhaust gas flows through the piping run, transferring heat from the exhaust gas to the process gas as the process gas flows through the piping run, and allowing the process gas to flow through a piping outlet physically connected to the piping run.

In certain aspects, the process gas is an acid gas feed. In certain aspects, the process gas is an air feed. In certain aspects, the piping outlet is fluidly connected to a convection section of the heat recovery furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the scope will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments and are therefore not to be considered limiting of the scope as it can admit to other equally effective embodiments.

FIG. 1 is a plan view of an embodiment of the heat recovery furnace of the heat recovery system.

FIG. 2 is a plan view of an embodiment of heat recovery system with a spiral piping configuration.

FIG. 3A is a plan view of an embodiment of heat recovery system with a wraparound piping configuration.

FIG. 3B is a top view of an embodiment of heat recovery system with a wraparound piping configuration.

FIG. 3C is a plan view of an embodiment of heat recovery system with a wraparound piping configuration.

FIG. 4A is a plan view of an embodiment of heat recovery system with a spiral piping configuration.

FIG. 4B is a plan view of an embodiment of heat recovery system with a spiral piping configuration.

FIG. 4C is a plan view of an embodiment of heat recovery system with a wraparound piping configuration.

FIG. 5 is a process flow diagram of an embodiment of heat recovery system.

FIG. 6 is a process flow diagram of an embodiment of heat recovery system.

FIG. 7 is a process flow diagram of an embodiment of heat recovery system.

FIG. 8 is a process flow diagram of an embodiment of heat recovery system.

DETAILED DESCRIPTION

While the scope of the apparatus and method will be described with several embodiments, it is understood that one of ordinary skill in the relevant art will appreciate that many examples, variations and alterations to the apparatus and methods described here are within the scope and spirit of the embodiments.

Accordingly, the embodiments described are set forth without any loss of generality, and without imposing limitations, on the embodiments. Those of skill in the art understand that the scope includes all possible combinations and uses of particular features described in the specification.

Provided are systems and methods for recovering heat from flue gases of a furnace to increase the temperature of process gases. The systems and methods for recovering heat from flue gases of a furnace can be used to pre-heat process streams before the process streams are introduced to the furnace. The systems and methods described here are directed to the use of piping through which heat can be transferred from flue gas flowing through the stack section of a furnace to a process gas flowing through the piping.

Advantageously, the systems and methods described here result in a decreased fuel gas load required in the furnace convection section. The reduced fuel gas load can result in a decreased amount of nitric oxides, including nitric oxide and nitrogen dioxide, and other emissions. Advantageously, the systems and methods described here do not block or impede the flow of the exhaust gas through the stack section.

As used here, “helix-shaped pipe” refers to piping shaped in helix around a helical axis. Helix-shaped pipe has a pipe diameter, outer helix diameter, a length, and a pitch. The pitch is the distance of one complete helix turn. Spiral length refers to the height of helix-shaped pipe from the inlet to the outlet as measured along the helical axis. Straight length refers to the length of the helix-shaped pipe if the helix-shaped pipe was straightened from inlet to outlet.

As used here, “minimally obstruct” means less than 50 percent of a flow path is obstructed by a physical obstruction, alternately less than 40 percent is obstructed, alternately less than 30 percent of a flow path is obstructed, and alternately less than 25 percent of a flow path.

As used here, “perimeter” means the length around a closed figure.

Referring to FIG. 1, an embodiment of a heat recovery furnace is provided. Heat recovery furnace 100 includes radiant zone 105, convection zone 110, and stack zone 120. Heat recovery furnace 100 can be any type of furnace with an exhaust stack that vents flue gases resulting from combustion. In at least one embodiment, heat recovery furnace 100 is a natural draft, box type fired-furnace. Fuel gas and air are burned in radiant zone 105 to maintain a continuous flame. The flame generates heat which increases the temperature in convection zone 110. The exhaust gas, containing the products of the reaction when the fuel gas is burned, exits convection zone 110 and enters stack zone 120 through stack inlet 122. The exhaust gas flows through stack zone 120 and exits stack outlet 124. Stack zone 120 is defined by wall 126. In at least one embodiment, stack zone 120 can be a length of pipe having a cylindrical shape, where wall 126 defines a circle and the perimeter around stack zone 120 is the circumference of the circle. In at least one embodiment, stack zone 120 can have a shape other than a cylinder, such that wall 126 defines a polygon and the perimeter around stack zone 120 is measured by the length of each edge of the polygon. The temperature of the exhaust gas in stack zone 120 can have a temperature greater than 800 degrees Fahrenheit (deg F.), alternately greater than 900 deg F., and alternately greater than 1000 deg F.

Piping system 130 can be positioned in stack zone 120. Piping system 130 includes piping run 132, piping inlet 134, and piping outlet 136. Piping run 132 can include spiral piping, wraparound piping, and combinations of the same. Piping system 130 is designed to minimally obstruct the flow of the exhaust gas. Because heat recovery furnace 100 is a natural draft, box type fired-furnace, the air is supplied to the furnace without an air blower or unit to force the air into the box resulting in a low pressure in the box. Obstructing the flow of the exhaust gas through the stack zone limits the ability to supply fresh air to the furnace without the addition of a pressure unit, such as an air blower. Piping system 130 does not include pipes transecting stack zone 120.

Piping inlet 134 transects wall 126 providing fluid communication between pipe external to stack zone 120 and piping run 132. Piping inlet 134 can be any type of configuration allowing fluid communication between the exterior and interior of a vessel. Piping inlet 134 can include pipe sections, nozzles, flanges, valves, and other fittings. The components of piping inlet 134 can be any materials of construction capable of containing the gas composition and withstanding the temperatures in fired furnace 100. The components of piping inlet 134 can be sized based on the flow rate of the gas flowing through piping inlet 134. Piping inlet 134 can be physically and fluidly connected to piping run 132. Piping inlet 134 can be located at any point in stack zone 120 between stack inlet 122 and stack outlet 124. In at least one embodiment, piping inlet 134 can be located proximate to stack inlet 122. In at least one embodiment, piping inlet 134 can be located proximate to stack outlet 124.

Piping outlet 136 transects wall 126 providing fluid communication between piping run 132 and pipe external to stack zone 120. Piping outlet 136 can be any type of configuration allowing fluid communication between the exterior and interior of a vessel. Piping outlet 136 can include pipe sections, nozzles, flanges, valves, and other fittings. The components of piping outlet 136 can be any materials of construction capable of containing the gas composition and withstanding the temperatures in fired furnace 100. The components of piping outlet 136 can be sized based on the flow rate of the gas flowing through piping outlet 136. Piping outlet 136 can be physically and fluidly connected to piping run 132. Piping outlet 136 can be located at any point in stack zone 120 between stack inlet 122 and stack outlet 124. In at least one embodiment, piping outlet 136 can be located proximate to stack inlet 122. In at least one embodiment, piping outlet 136 can be located proximate to stack outlet 124.

In at least one embodiment, as described with reference to FIG. 2 and FIG. 1, piping run 132 includes spiral piping 140. Piping inlet 134 transects wall 126 at a location proximate to stack outlet 124 and is connected to spiral piping 140. Spiral piping 140 contains helix-shaped pipe. The pipe diameter and material of construction for spiral piping 140 can be based on the gas volumetric flow rate and composition of gas in spiral piping 140. The straight length of helix-shaped pipe can be determined based on the volume of gas, the residence time, and the amount of heat energy to be captured. The pitch along spiral piping 140 can be determined based on the increase in temperature desired in the gas flowing through spiral piping 140 in consideration of the straight length. Spiral piping 140 can extend from piping inlet 134 adjacent to wall 126 to piping outlet 136. Positioning spiral piping 136 adjacent to wall 126 results in spiral piping 136 having an outer helix diameter approaching the inner diameter defined by the interior of wall 126. By running adjacent to wall 126, spiral piping 140 does not block the bulk of the flow of exhaust gas rising from convection zone 110 through stack zone 120. While the exhaust gas can flow in the gap between spiral piping 140 and wall 126, the bulk of the exhaust gas flows through the section defined by the inner helix diameter. Spiral piping 140 can be in contact with wall 126 or there can be a gap between spiral piping 140 and wall 126. The gap between outer helix diameter of spiral piping 140 and inner diameter of wall 126 can be less than 2 inches (5.08 centimeters (cm)), alternately less than 1.5 inches (3.81 cm), alternately less than 1 inch (2.54 cm), and alternately less than 0.5 inches (1.27 cm) as measured at operating conditions. The spiral length can be the same as the height of the stack zone 120 as measured from stack inlet 122 to stack outlet 124, and alternately can be less than the height of the stack zone. Spiral piping 140 is fluidly and physical connected to piping outlet 136 which transects wall 126 at a location proximate to stack inlet 122.

In at least one embodiment, as described with reference to FIG. 3A-C and FIG. 1, piping run 132 includes wraparound piping 150. Wraparound piping 150 can include piping components that can include pipe sections, elbows, and other fittings as needed to meet the design specifications, including diameter and length, for piping rise 152, piping loop 154, and piping down-run 156. The piping components of wraparound 150 can be any materials of construction capable of containing the gas composition and withstanding the temperatures in fired furnace 100. The diameter of the piping components of wraparound piping 150 can be sized based on the flow rate of the gas flowing through wraparound piping 150. Wraparound piping 150 can be positioned adjacent to wall 126, such that wraparound piping 150 does not block the bulk of the flow of exhaust gas flowing from convection zone 110 through stack zone 120.

Piping inlet 134 transects wall 126 proximate to stack inlet 122. Piping inlet 134 connects physically and fluidly to piping rise 152 of wraparound piping 150. Piping rise 152 extends from piping inlet 134 to piping loop 154 adjacent to wall 126 for a rise height. The rise height of piping rise 152 can be the length of stack zone 120 as measured from stack inlet 122 to stack outlet 124, alternately any length less than the length of stack zone 120. Piping rise 152 can be in contact with wall 126 or there can be a gap between piping rise 152 and wall 126. The gap between piping rise 152 and wall 126 can be less than 2 inches (5.08 centimeters (cm)), alternately less than 1.5 inches (3.81 cm), alternately less than 1 inch (2.54 cm), and alternately less than 0.5 inches (1.27 cm) as measured at operating conditions.

Piping loop 154 is positioned parallel to the plane that intersects stack zone 120, perpendicular to piping rise 152. The length of piping loop 154 can be equal to the perimeter of stack zone 120 less the diameter of piping rise 152 and the diameter of piping down-run 154 and any fittings connecting piping loop 154 to piping rise 152 and piping down-run 154, alternately less than the perimeter of stack zone, alternately less than three-quarters of the perimeter of stack zone 120, alternately less than one-half of the perimeter of stack zone 120, and alternately less than one-quarter of the perimeter of stack zone 120. The length of piping loop 154 can be based on the total length desired for wraparound piping 150, the location of inlet piping 134 and outlet piping 136, the perimeter of stack zone 120, and combinations thereof. At a minimum, the length of piping loop 154 is equal to the combined length of the outer diameter of piping rise 152 and the outer diameter of piping down-run 154. Piping loop 154 is located adjacent to wall 126. Piping loop 154 can be in contact with wall 126 or there can be a gap between piping rise 152 and wall 126. The gap between piping loop 154 and wall 126 can be less than 2 inches (5.08 centimeters (cm)), alternately less than 1.5 inches (3.81 cm), alternately less than 1 inch (2.54 cm), and alternately less than 0.5 inches (1.27 cm).

Piping loop 154 connects physically and fluidly to piping down-run 156 of wraparound piping 150. Piping down-run 156 extends from piping loop 154 to piping outlet 136 adjacent to wall 126 for a down-run height. The down-run height of piping down-run 156 can be the length of stack zone 120 as measured from stack inlet 122 to stack outlet 124, alternately any length less than the length of stack zone 120. The down-run height of piping down-run 156 can be same as the rise height of piping rise 152, alternately can be less than the rise height, and alternately can be greater than the rise height. Piping down-run 156 can be in contact with wall 126 or there can be a gap between piping down-run 156 and wall 126. The gap between piping down-run 156 and wall 126 can be less than 2 inches (5.08 centimeters (cm)), alternately less than 1.5 inches (3.81 cm), alternately less than 1 inch (2.54 cm), and alternately less than 0.5 inches (1.27 cm). Piping outlet 134 transects wall 126 proximate to stack inlet 122.

While the exhaust can flow in the gaps between piping rise 152, piping loop 154, and piping down-run 156 and wall 126, the bulk of the exhaust gas flows through the center of stack zone 120.

Piping run 132 can include spiral piping, wraparound piping, and combinations of the same. Referring to FIGS. 4A and 4B, piping run 132 can include one or more spiral piping configurations. As shown in FIG. 4A, piping run 132 can have a double helix configuration. As shown in FIG. 4B, piping run 132 can be two single helixes stacked on top of each other. Referring to FIG. 4C, piping run 132 can include one or more wraparound piping configuration. As shown in FIG. 4C, piping run 132 can include two wraparound piping configurations. Although shown with piping inlet 134 and piping outlet 136 in parallel, it is understood that the physical configuration of piping run 132 containing one or more wraparound piping configuration can be determined based on the physical space limitations of the plant.

The heat recovery furnaces described can be used in process where a traditional fired-heater is used. Advantageously, existing fired-heaters can be retrofitted to incorporate the piping systems described here to create a heat recovery furnace. Processes that can utilize heat recovery furnaces can include gas plant processes, crude oil processing units, hydrocracking units, and sulfur recovery units.

Referring to FIG. 5, a method of using the heat recovery furnaces in a sulfur recovery unit is provided. Pre-heat system 1 includes acid gas pre-heater 200 and air pre-heater 300. Pre-heat system 1 can be used to perform a two-step of pre-heating of both the air feed and the acid gas feed to sulfur recovery unit 400. Acid gas pre-heater 200 can be a heat recovery furnace as described with reference to FIG. 1. Air pre-heater 300 can be a heat recovery furnace as described with reference to FIG. 1.

Air feed 10 can be introduced to stack zone 220 of acid gas pre-heater 200 through air stage 230. Air stage 230 can be a piping system as described with reference to FIGS. 1-4. The temperature of air feed 10 can be increased in air stage 230 to produce pre-heated air feed 12.

Pre-heated air feed 12 can be introduced to stack zone 320 of air pre-heater 300 through air piping 330. Air piping 330 can be a piping system as described with reference to FIGS. 1-4. The temperature of pre-heated air feed 12 can be increased in air piping 330 to produce air heater feed 14.

Air heater feed 14 can be introduced to a convection section of air pre-heater 300. The temperature of air heater feed 14 can be increased in the convection section of air pre-heater 300 to produce hot air feed 16. Hot air feed 16 can be at the temperature required for sulfur recovery unit 400.

Acid gas 20 can be introduced stack zone 320 of air pre-heater 300 through gas piping 340. Gas piping 340 can be a piping system as described with reference to FIGS. 1-4. The temperature of acid gas 20 can be increased in gas piping 340 to produce pre-heated acid gas 22.

Pre-heated acid gas 22 can be introduced to stack zone 220 of acid gas pre-heater 200 through gas stage 240. Gas stage 240 can be a piping system as described with reference to FIGS. 1-4. The temperature of pre-heated acid gas 22 can be increased in gas stage 240 to produce acid gas heater feed 24.

Acid gas heater feed 24 can be introduced to a convection section of acid gas pre-heater 200. The temperature of acid gas heater feed 24 can be increased in the convection section of acid gas pre-heater 200 to produce hot acid gas feed 26. Hot acid gas feed 26 can be at the temperature required for sulfur recovery unit 400.

Pre-heating the acid gas feed and the air feed results in less heat energy being required to reach the temperature required for operation of the sulfur recovery unit. Less heat energy translates to less volume of fuel gas required as compared to a conventional fired-heater, thus the efficiency of the heat recovery furnaces is increased compared to a conventional fired-heater.

Sulfur recovery unit 400 can be any type of unit capable of recovering sulfur from an acid gas stream. Sulfur recovery unit 400 can include reaction furnace 410, waste heat boiler 420, condenser 430, and catalytic stage 440.

The components of hot acid gas feed 26 and the components of hot air feed 16 react in reaction furnace 410 to produce reaction effluent 415. Reaction effluent 415 can include elemental sulfur, sulfur dioxide, hydrogen sulfide, air, and combinations of the same. Reaction effluent 415 is introduced to waste heat boiler 420. The temperature of reaction effluent 415 can be reduced in waste heat boiler 420 to produce boiler effluent 425. Boiler effluent 425 can be introduced to condenser 430. The temperature of boiler effluent 425 can be reduced in condenser 430 to produce liquid sulfur 450 and cooled gases stream 435. Liquid sulfur 450 can include elemental sulfur. Cooled gases stream 435 can include sulfur dioxide, hydrogen sulfide, air, and combinations of the same. Cooled gases stream 435 can be introduced to catalytic stage 440. Catalytic stage 440 can include one or more catalytic reactors, followed by one or more condensers and one or more reheaters. Catalytic stage 440 can produce discharge 445 and sulfur stream 455. Discharge 445 can include the gases that do not react in catalytic stage 440. Discharge 445 can include sulfur dioxide, hydrogen sulfide, air, and combinations of the same. Sulfur stream 455 can include elemental sulfur.

Referring to FIG. 6, with reference to FIGS. 1 and 5, a heat integration process using the heat recovery furnaces with a sulfur recovery unit is provided. Air feed 10 can be introduced to the convection section of air heater 600. Air heater 600 can be a heat recovery furnace as described with reference to FIG. 1. The temperature of air feed 10 can be increased in air heater 600 to produce hot air feed 16. Hot air feed 16 can be introduced to reaction furnace 410 of sulfur recovery unit 400.

Acid gas 20 can be introduced to the convection section of acid gas heater 500. Acid gas heater 500 can be a heat recovery furnace as described with reference to FIG. 1. The temperature of acid gas 20 can be increased in acid gas heater 500 to produce hot acid gas feed 26. Hot acid gas feed 26 can be introduced to reaction furnace 410.

Cooled gases stream 435 can be introduced to gas piping system 530 of acid gas heater 500. The temperature of cooled gases stream 435 can be increased in gas piping system 530 to produce gases stream 535. Gas piping system 530 can be a piping system as described with reference to FIGS. 1-4.

Gases stream 535 can be introduced to air piping system 630 of air preheater 600. The temperature of gases stream 535 can be increased in air piping system 630 to produce hot stream 635. Air piping system 630 can be a piping system as described with reference to FIGS. 1-4.

The temperature of hot stream 635 can be between 300 deg F. (148 deg C.) and 450 deg F. (232 deg C.), alternately between 350 deg F. (176 deg C.) and 400 deg F. (204 deg C.), and alternately between 365 deg F. (185 deg C.) and 385 deg F. (196 deg C.). Hot stream 635 can be introduced to catalytic stage 440.

Referring to FIG. 7, with reference to FIGS. 1, 5, and 6, a heat integration process using heat recovery furnaces with a sulfur recovery unit is provided. Gases stream 535 can be introduced to catalytic stage 440. The temperature of gases stream 535 can be between 300 deg F. (148 deg C.) and 450 deg F. (232 deg C.), alternately between 350 deg F. (176 deg C.) and 400 deg F. (204 deg C.), and alternately between 365 deg F. (185 deg C.) and 385 deg F. (196 deg C.).

Referring to FIG. 8, with reference to FIGS. 1, 5, and 6, a heat integration process using heat recovery furnaces with a sulfur recovery unit is provided. Cooled gases stream 435 can be introduced to air piping system 630 of air preheater 600. The temperature of cooled gases stream 435 can be increased in air piping system 630 to produce hot stream 635. The temperature of hot stream 635 can be between 300 deg F. (148 deg C.) and 450 deg F. (232 deg C.), alternately between 350 deg F. (176 deg C.) and 400 deg F. (204 deg C.), and alternately between 365 deg F. (185 deg C.) and 385 deg F. (196 deg C.). Hot stream 635 can be introduced to catalytic stage 440.

The temperature of gases stream 535 and the temperature of hot stream 635 can be designed to maximize conversion of sulfur dioxide and hydrogen sulfide in catalytic stage 440 to elemental sulfur while increasing the efficiency of the process.

Advantageously, the incorporation of heat recovery furnace with a sulfur recovery unit can optimize the fuel gas consumption in the process.

Although the embodiments have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope. Accordingly, the scope of the embodiments should be determined by the following claims and their appropriate legal equivalents.

There various elements described can be used in combination with all other elements described here unless otherwise indicated.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed here as from about one particular value to about another particular value and are inclusive unless otherwise indicated. When such a range is expressed, it is to be understood that another embodiment is from the one particular value to the other particular value, along with all combinations within said range.

As used here and in the appended claims, the words “comprise,” “has,” and “include” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. 

That which is claimed is:
 1. A piping system for recovery heat energy from an exhaust gas in a heat recovery furnace, the piping system comprising: a piping inlet, where the piping inlet transects a wall of a stack zone of the heat recovery furnace; a piping run, the piping run fluidly connected to the piping inlet; and a piping outlet, the piping outlet fluidly connected to the piping run, where the piping outlet transects the wall of the stack zone of the heat recovery furnace, where the piping system is positioned in a stack zone of the heat recovery furnace between a stack inlet and a stack outlet.
 2. The piping system of claim 1, where the piping run is spiral piping comprising helix-shaped pipe, where the piping inlet transects the wall proximate to the stack outlet of the heat recovery furnace, where the piping outlet transects the wall proximate to the stack inlet of the heat recovery furnace, and where there is a gap between the spiral piping and the wall.
 3. The piping system of claim 2, where the gap is less than 2 inches.
 4. The piping system of claim 1, where the piping run is wraparound piping, the wraparound piping comprising: a piping rise, the piping rise fluidly connected to the piping inlet, where the piping rise has a rise height; a piping loop, the piping loop fluidly connected to the piping rise, where the piping loop is located adjacent to the wall, where the piping loop has a length; and a piping down-run, the piping down-run fluidly connected to the piping loop and further fluidly connected to the piping outlet, where the piping down-run has a down-run height.
 5. The piping system of claim 4, where the rise height is less than the distance between the stack inlet and the stack outlet.
 6. The piping system of claim 4, where the length of the piping loop is less than the perimeter of the stack zone.
 7. The piping system of claim 4, where the down-run height is less than the distance between the stack inlet and the stack outlet.
 8. The piping system of claim 1 further comprising two piping runs.
 9. A method of recovering heat from an exhaust gas in a stack zone of a heat recovery furnace, the method comprising the steps of: introducing a process gas through a piping inlet, where the piping inlet transects a wall of the stack zone; allowing the process gas to flow through a piping run physically connected to the piping inlet, where the piping run is positioned in the stack zone between a stack inlet and a stack outlet, where the piping run is positioned adjacent to the wall such that the exhaust gas flows through the piping run; transferring heat from the exhaust gas to the process gas as the process gas flows through the piping run; and allowing the process gas to flow through a piping outlet physically connected to the piping run.
 10. The method of claim 9, where the piping run is spiral piping comprising helix-shaped pipe, where the piping inlet transects the wall proximate to the stack outlet of the heat recovery furnace, where the piping outlet transects the wall proximate to the stack inlet of the heat recovery furnace, and where there is a gap between the spiral piping and the wall.
 11. The method of claim 10, where the gap is less than 2 inches.
 12. The method of claim 9, where the piping run is wraparound piping, the wraparound piping comprising: a piping rise, the piping rise fluidly connected to the piping inlet, where the piping rise has a rise height; a piping loop, the piping loop fluidly connected to the piping rise, where the piping loop is located adjacent to the wall, where the piping loop has a length; and a piping down-run, the piping down-run fluidly connected to the piping loop and further fluidly connected to the piping outlet, where the piping down-run has a down-run height.
 13. The method of claim 12, where the rise height is less than the distance between the stack inlet and the stack outlet.
 14. The method of claim 12, where the length of the piping loop is less than the perimeter of the stack zone.
 15. The method of claim 12, where the down-run height is less than the distance between the stack inlet and the stack outlet.
 16. The method of claim 9, where the process gas is an acid gas feed.
 17. The method of claim 9, where the process gas is an air feed.
 18. The method of claim 9, where the piping outlet is fluidly connected to a convection section of the heat recovery furnace. 